Railway signaling system



May 4, 1943. H. A. THOMPSON RAILWAY SIGNALING SYSTEM Filed Dec 7, 1940 15DZ' J Y 12/ 1! I B c EMT I l l f 0X 6X TIL 322mm mm Mm TI,-

Fig. 7.

INVENTOR Howard lzomprozz.

HIS ATTORNEY Patented May 4, 1943 ()FFICE RAELWAY SIGNALING SYSTEMI Howard A. Thompson, The Union Switch Edgewood, Pa., assignor to & Signal Company, Swissval e, Pa, a corporation of Pennsylvania Application December '7, 1940, Serial No. 369,004

8 Claims.

My invention relates to railway signaling apparatus and particularly to systems of the type employing alternating current and single element track relays in the track circuits thereof.

Signaling systems of this type must be so designed that if an insulated joint separating two track sections becomes defective, energy supplied to one section cannot feed across the defective joint and produce a false operation of the track relay for an adjoining section.

It has heretofore been suggested to prevent this objectionable feeding of energy from one track section to another by providing a lockout circuit todiscontinue the supply of coded energy if a joint is defective, or by providing special forms of insulated joints or track circuit connections. It is an object of my invention to provide a signaling system of the type having track circuits employing alternating current and having single element track relays, the system being arranged to prevent response of the track relay of each section to energy feeding across a defectivc joint from another section.

A further object of my invention is toprovide a system of the type described and in which the alternating current energy supplied to the various track sections is modified so that the impulses of energy of one relative polarity therein are of substantially larger value than those of the other relative polarity so that a track relay of the direct current type may be employed.

A further object of my invention is to provide a system of the type described'and employing direct current track relays of a type which are responsive only to energy of one relative polarity and having the track circuits of adjoining sections arranged so that the track relays thereof respond to energy of opposite polarity to'thereby prevent response of a relay to energy feeding over a defective joint from an adjacent section.

Another object of my invention is to provide a system of the type described employing in the track circuits thereof a modified form of alterhating current energy which will operate track relays oi the direct current type and which will also eifect operation of the standard forms. of inductive cab signal apparatus carried by locomotives traversing the track stretch.

A further object of invention is to provide means for supplying modified alternating current energy of the type reauired for use in a system of the kind: mentioned above.

Other objects of my invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawing. 1

I shall describe one form of signaling system embodying my invention, together withse'veral modified forms of apparatus which I may employ in this system, and'shall then point out the novel features thereof in claims.

In the drawing Fig. 1 is a diagram showing a stretch of railway track equipped with the signaling system provided by this invention;

Fig. 2 is a diagram of a typical alternating current voltage curve;

Fig. 3 is a diagram of the voltage curve of the alternating current employed in the system provided by my invention; and

Figs. 4 to 7 are diagrams showing other means which may be employed to provide the modified alternating current energy employed in this system.

Similar reference characters refer to similar parts in each of the several views.

Referring to Fig. 1 of the drawing, there is shown therein a stretch of railroad track having track rails l and 2 over which trailic normally moves in the direction indicated by the arrow, that is from left to right. The rails of the track stretch are divided by insulated joints into the customary track sections. Two complete sections designated HT and I3T, together with portions of the adjoining sect-ions HT and MT are shown. v I

Each track section has at the entrance end thereof a signal S for indicating the nature of trafiic conditionsin;advance. As shown, these signals are of the color light type andeach' is provided with a red or stoplampR, a yellow or caution lamp Y, and a greenor clear lamp G. While the system is illustrated as employing signals of the color light type, it should be understood that any type of signal may be employed, and also that the invention is applicable to track stretches without wayside signals and having cab signals only.

The rails of each of the track sections form a part of a track circuit to which coded alternating current of a modified form, as hereinafter explained, is continuously supplied. The signaling system shown is of the three indication variety and makes use of energy coded at two code frequencies, namely 75 and 180 energy impulses a minute which are separated by periods 'of equal duration during which no energy is supplied. The coded energy .is provided bycode transmitters CT which have contacts '75 and 180 which are continuously actuated by a motor or other means.

The alternating current energy employed in this system may be supplied from any suitable source, such as a commercial source of current, and may be distributed throughout the track stretch by a transmission line, not shown. If energy from a commercial source is not available, the alternating current may be: generated locally by tuned reed alternators. In the drawing the terminals of the source of alternating current are designated BX and GK, and it will be assummed that this energy is of a suitable frequency, such as 60 cycles per second.

Each of the track sections has at the entrance end thereof a code following track relay TR which is of the direct current type and incorporates a permanent magnet which renders the relay responsive only to energy which is predominantly of .one relative polarity and nonresponsive to energy predominantly of the other relative polarity. A relay of the type which I may employ is shown in United States Patent No. 1,959,562, issued May 22, 193A, to Harry E. Ashworth.

Each of the track relays has associated therewith a decoding transformer DT and auxiliary relays H and J. A contact 20 of each track relay controls the supply of energy from a local source of direct current, not shown, to the primary winding of the associated decoding transformer, while a contact 21 of each track relay rectifies the energy supplied from one secondary winding of the associated transformer to the associated relay H so that the relay H is energized when and only when the track relay is responding to coded energy.

Each decoding transformer is also provided with another secondary winding from which energy is supplied to the relay J through a suitable resonant rectifier unit which is arranged to permit sufficient energy to be supplied to the relay J to pick up the relay contact only when the energy induced in the decoding transformer secondary winding is of the frequency present when the track relay is responding to energy of the 180 code frequency.

Each track section is supplied with coded alternating current energy through a track transformer TT, while the primary winding of a transformer MT is connected in series with the connection of one terminal of the secondary winding of the track transformer TT to one of the track rails. The secondary winding of each transformer MT is short circuited through a rectifier or asymmetric unit K.

On the flow of energy through the primary winding of a transformer MT energy is induced in the transformer secondary winding. During the half cycles in which the energy induced in the secondary winding of transformer MT is of one relative polarity the energy can flow freely through the rectifier K so that the transformer secondary winding is short circuited, thereby reducing the impedance of the transformer primary winding with the result that energy may flow freely through this winding from the track transformer TT to the track rails.

However, during the half cycles in which the energy induced in the secondary winding of transformer MT is of the other relative polarity. the' rectifier K prevents short circuiting of the secondary winding of the transformer MT with the result. that the impedance of the primary winding of this transformer is relatively high and offers considerable resistance to the flow of energy from the track transformer T1 to the track rails.

It will be seen, therefore, that the action of the transformers MT is to modify the alternating current energy supplied to the track rails so that the impulses of energy of one relative polarity are of substantially greater value than those of the other relative polarity. The effect of the transformer MT is clearly shown in Figs. 2 and 3 of the drawing.

Fig. 2 is a diagram showing a typical alternating current voltage curve. This is the type of energy which would be supplied to the track rails if the transformers MT were not employed.

Fig. 3 is a diagram showing the voltage of the energy supplied through the transformer MT. As shown in this diagram, the impulses of energy of one relative polarity are of substantially greater value than those of the other relative polarity. To bring out the difference in the value of the impulses of different polarities, there is shown in broken lines, under the curve for the impulses above the zero line, the value which these impulses would have if they were equal to the impulses below the zero line.

As the impulses of energy of one relative polarity substantially exceed in value those of the other relative polarity, the energy supplied to the track rails has a direct current component which is equal to the difference in the value of the impulses of different polarities. This direct current component is effective to operate a direct current code following relay, while it has been found that the modified alternating current energy will produce proper operation of inductive cab signal apparatus carried by locomotives traversing the track stretch. The details of construction and operation of the locomotive cab signal equipment are not a part of the invention. One form of equipment which may be employed on the locomotives is shown in United States Patent No. 1,986,679, issued January 1, 1935, to Lloyd V. Lewis.

The track relays TR are of a type which respond only to direct current of one relative polarity, and the equipment is arranged so that the direct current component of the modified alternating current supplied to the track rails of each section is of the proper polarity to operate the track relay for that section. The relative polarity of the direct current component of the energy supplied to each section is indicated in the drawing by the usual designations.

In order to prevent operation of a track relay by energy feeding over a defective joint the direct current component of the energy employed in adjoining track sections is of opposite relative polarities.

. The equipment is shown in Fig. 1 of the drawing in the condition which it assumes when the track stretch is vacant. At this time coded alternating current energy of code frequency is supplied to the primary winding of the track transformer I3TT over a. circuit controlled by apparatus, not shown, associated with section On the supply of energy to the transfermer I3T'I coded alternating current of a modified form is supplied through the transformer EBMT to the rails of section [3T and to the relay 13TH.

. As pointed out above, the direct current component of the alternating current energy is such that the track relay I3TR will respond to this energy. Accordingly, during; the; on. intervals in the code the contacts of. the track relay MFR are. picked up, while they are released during. the oiTinter-Vals in the code. As a. result. of; this code following operation of the trackrelay l3;'I,R, energy is supplied through the decoding. transformer |=3DT to the relays. tSH and I35 and the contacts-of. these-relays; are. picked up and. establishthe circuit of the green lamp- G of signal lz3S. In addition, as; contact 25, of relay [3H is picked up; thecircuit oi the LS3 contact of code transmitter [336T is established so that energy oi. this code frequency is supplied to,- the rails: of section lZ-T. As a result, Signal LES displays its green or clear-indication. while energy of the it? codefrequency is supplied to; the rails of section H T.

When a train moving inthe rzlorn-lalv direction of tra-fiic; that is from left. to right, enters section, lZT, the trackrelay- LZTR- is shunted and energyis no longer supplied through thedecodingv transformer l-2D-I= to the relays: tZl-I and 25. and these relays release, thereby interrupting the circuit of the green lampG: and establishing the circuit of the red lamp R of signal. [28. In addition,

on release of contact 25 of relay 82H. the -ircuit of the 180 contact codetransmitter 5-28! is interrupted and the circuit. of the 75 con-* established sothat the energysuppli d tos 1 UP is changed from 18.9 to 75 code frequency.

Likewise, when the train enters section lQ-T, the signal its is caused to display itsv stop indication, while energy of '7-5 frequencyis supplied to the rails of section 52?). When the train vacates section LET, the track relay iZTR responds to this energyand current is. supplied through the decoding transtormer i-ZDT to. pick up. the relay IEH, but i-nsufficien energy.- is supplied through. the resonant unit to pick up relay L21. Accordingly, the signal L25 lays its yellow or caution indie Lon, while one. Myof- 180. code frequency is suppl d to section HT.

Similarly, when the tra n vacates section 5ST, energy of. '75 code frequency feeds tothetrack relay ISTR and the signal: HES is conditioned to display its caution; indication, whileenergy of 180. code frequency is supp tosectionlZT so that the signal its display s green indication. When the train vacates. se ion- MT, signalz its is. also conditioned to display its. green clear indication.

On movement of a. locomotive equipped with cab. signal apparatus through the track stretch the. cab signal. equipment willrespond. the usual manner to the coded alternating.- cur supplied. to. the track. rails. of the various track sections. to. provide. the proper cab signal aspect,

In the system provided by this invention. direct current track relaysresponsive to energy of one polarity only areemployed, while the trackcircuits are. arranged so that the direct current component. of the energy in adjoining track sections is. of opposite relative polarity... Thus. insection I231 track rai-l I. is. negative and. track rail 2, is positive, while in section 3T track rail l is. positive and track rail 2. is negative...

When a train is present. in section. l the track relay ISTR. should be shunted and should not respond to coded energy. If at. this time the insulated joints 3 separating sections; 521

mainreleased; while: the: signal lsswoifld con;- tinuato display its. red; or stop indication. Similarly, the: insulated: joints separating any other two sections should be. cheiectiyev so that energy from one section feeds; to the track; relay of the other; the trackrelay will not respend: tothis energy and. will; not: improperly condition. a signal; to. display a. proceed indicati'on..

Inthe. system: shown in; Fig... I of the drawing; there is shown one means for; providing.- the modified; alternating: current with. a direct cur rent. component which is required in this system. This energy maybe. provided in other ways, and: Fi'gsA to 7 show other means for pro viding this energy.

In the system shown in Fig; 1- of. the: drawing the transformer MT has its primary Winding; connected in series with the secondary;wind.-v ing. of the track transformer. The modification shown. in; Fig, 4; is similar." to that shown in 1-. and employs: a transformer NT having its pri-= marywinding connected in multiple. with the; secondary winding of the track transformer The terminals of the secondary winding of" the transformer are connected. together through a resistance 2.6; and a. recti'fier'K.

Accordingly; when impulses of energy of one relative; polarity are: induced: in thesecondary windingof transformer current flows through the: rectifier K and is dissipated: by the resistance 2.6:. At thisti-me, therefore, a past of the energy supplied from the secondary winding: of the track transformer.-

is; consumed by the transformer NfT- so that the value of the impulses. of energy supplied-to; the track rails is less than they wouldsbe if the transformer were; not: present.

When impulses of: energy .of' the: opposite relative polarity are induced in; the secondary wind.- ing of the transformer NT, they are prevented from flowing; the. resistance lit. by the: rectifier K. Accordingly. at, this time the transformer takes little; or no. energy from the: tracktranstormerT-T and the impulses of; energy supplied to the track rails. are of substantiallythe full valuesupplied from the; track transa' former 'IT;

As the modification shown inFi-g. 4 operates to provide; impulses of one, polarity which are or substantially higher value than those oi the 7 other polarity, the alternating current supplied to. the track rails has a direct current component which; will operate a. direct current code renewing trackit relay as explained in; common on with Fig;- 1.

In- Fig. 5. theseis shown another means tor providing the3 modified alternating current. em ployed in this system; In; this modification one terminal of the secondary finding of." the track transformer 'IT' is eonnectedto. one of the. track rails; through a resistance 28', while this resistance is shunted. bya: circuit including a'rectifier or asymmetric unit K.

When impulses of energy of one relative po larity ar induced. in the secondar winding of the track transformer, they are prevented from flowing through? the rectifier K so that the ener y supplied to the, track rails is supphed through the resistance 28 and is diminished. thereby;

When impulses of the other relative polarity are induced inthe track transformer secondary winding, they mayflow treelythrough the rectt-i fier K to the. track'rails so that these impulses are not reduced in value by the resistance: flax Accordingly, the impulses of energy of opposite polarities supplied to the track rails are of unequal value so that the track circuit energy has a direct current component and will operate a direct current code following track relay.

The modification shown in Fig. 6 is similar to that shown in Fig. and has a resistance connected across the terminals of the track transformer secondary winding, while a rectifier K is connected in series with the resistance. When impulses of energy of one relative polarity are induced in the track transformer secondary winding, this energy may flow freely through the resistance 30 and the rectifier K so that a portion of these impulses are absorbed by the resistance. When impulses of energy of the other relative polarity are induced in the transformer secondary winding, they are prevented from flowing through the resistance 30 by the rectifier K and these impulses are supplied undiminished to the track rails. This modification operates, therefore, to provide impulses of energy of opposite polarities which are of unequal value so that the alternating current supplied to the track rails has a direct current component.

The modification shown in Fig. '7 shows another means for providing the track circuit energy employed in this system. This modification employs a special track transformer having two secondary windings 3| and 32 each of which is connected with the track rails in series with a rectifier or asymmetric unit K. The rectifier associated with winding 3| is poled to permit the supply of energy of one relative polarity to the track rails, while the rectifier associated with winding 32 is poled to permit the supply of energy of the other relative polarity. The windings 3| and 32 are proportioned so that the winding 32 has a substantially larger number of turns than the winding 3|, while the two windings are arranged so that energy of the same relative polarity is induced in each at the same time,

- When energy of one relative polarity is induced in the track transformer secondary windings, en-

ergy is supplied from the winding 3| to the track K rails, but not from the winding 32. Similarly, when energy of the opposite polarity is induced in the track transformer secondary windings, energy is supplied to the track rails from the winding 32, but not from the winding 3|. As the winding 32 has a substantially larger number of turns than the winding 3|, the impulses of energy supplied from the winding 32 to the track rails are of substantially higher value than those supplied from the winding 3|. Accordingly, the impulses of energy of one polarity supplied to the track rails substantially exceed in value those of the other relative polarity and the track circuit energy has a direct current component so that it will operate a direct current track relay.

. While the system provided by this invention has been illustrated and described in connection with a signaling system employing coded energy in the track circuits thereof, it is not restricted to use in such systems.

Although I have herein shown and described only one form of railway signaling system embodying my invention, together with several forms of apparatus which may be employed therein, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is: I

1. In a railway signaling system for use in track stretches over which are operated vehicles carrying signaling apparatus responsive to the flow of alternating current in the track rails, in combination, a stretch of railroad track having a pair of track rails divided by insulated joints into a plurality of track sections, a direct current track relay for each section having a winding connected across the rails of the associated section, a track transformer for each section, and means for each section for supplying from the transformer for the said section to the rails of such section impulses of energy of alternate relative polarity, each such means including a unidirectional impedance element and being arranged so the energy supplied from the transformer to the rails of the associated section includes impulses of energy of both polarities of substantial magnitude and also being arranged so that the potential of the impulses of one relative polarity supplied to the rails of the associated section is substantially higher than that of the impulses of the other relative polarity, whereby the energy supplied to said track rails is alternating in character so as to operate signaling apparatus on vehicles traversing the track stretch and is predominantly of one relative polarity so as to operate the track relays.

2. In a railway signaling system, in combination, a stretch of railroad track having a pair of track rails divided by insulated joints into a forward and a rearward section, each section having a direct current track relay having a winding connected across the rails of the associated section adjacent the entrance end thereof, said track relays being of a type which are responsive to energy of one polarity only, the relay for the forward section being responsive to energy of normal polarity and the relay for the rearward section being responsive to energy of reverse polarity only, a track transformer for each section, and means for each section for supplying from the transformer for the said section to the section rails adjacent the exit end of the section impulses of energy of alternate relative polarity, each such means including a unidirectional impedance element and being arranged so the energy supplied from the transformer to the rails of the associated section includes impulses of energy of both polarities of substantial magnitude and also being arranged so that the potential of the impulses of one relative polarity supplied to the rails of the associated section is substantially higher than that of the impulses of the other relative polarity, whereby the energy supplied to the rails of each of said sections is predominantly of one relative polarity and is effective to operate a track relay, the means for supplying energy to the rails of the forward section being arranged so that the impulses of energy of normal relative polarity predominate, the means for supplying energy to the rails of the rearward section being arranged so that the impulses of energy of reverse relative polarity predominate, whereby the track relay for each section will respond to energy supplied thereto from the supply means for such section and whereby the track relay for the forward sec tion will not respond to energy feeding thereto across defective insulated joints from the rails of said rearward section.

3. In a railway signaling system, in combination, a section of railway track having a pair of track rails, a direct current track relay having a winding connected across the section rails adjacent one end thereof, a track transformer located adjacent the other end of the section, means for supplying alternating current energy to the primary winding of said track transformer, said track transformer having one terminal of its secondary winding connected to one track rail of said section and having its other terminal connected to the other track rail in series with the primary winding of a modifying transformer, and a circuit including in series therewith an asymmetric unit for short circuiting the secondary winding of said modifying transformer, whereby the impedance of the primary winding of said modifying transformer to flow of impulses of energy of one polarity is greater than to the flow of impulses of energy of the other relative polarity, whereby the energy supplied from the track transformer is predominantly of one relative polarity and is effective to operate said track relay.

4. In a railway signaling system, in combination, a section of railway track having a pair of track rails, a direct current track relay having a winding connected across the section rails adjacent one end thereof, a track transformer located adjacent the other end of the section, means for supplying alternating current energy to the track transformer primary winding, said track transformer secondary winding having one of its terminals connected to one track rail and the other of its terminals connected to the other track rail of said section, a resistance included in series with the connection from one terminal of the track transformer to one track rail, and a circuit including an asymmetric unit in series therewith and shunting said resistance, whereby impulses of energy of one relative polarity are supplied from the track transformer to the track rails through said shunt circuit while impulses of energy of the other relative polarity are supplied to the track rails through the resistance, whereby the energy supplied to the track rails is predominantly of one relative polarity and is effective to operate said track relay.

5. In a railway signaling system, in combination, a section of railway track having a pair of track rails, a direct current track relay having a winding connected across the section rails adjacent one end thereof, a track transformer located adjacent the other end of the section, means for supplying alternating current energy to the primary winding of said track transformer, said track transformer having a first and a second secondary winding, one of said secondary windings being connected across the section rails in series with an asymmetric unit poled to permit energy of normal polarity to be supplied to the track rails, the other of said secondary windings being connected across the section rails in series with an asymmetric unit poled to permit energy of reverse relative polarity to be supplied to the track rails, whereby impulses of energy of one relative polarity are supplied from one of said secondary windings to the track rails and impulses of energy of the other relative polarity are supplied from the other of said secondary windings to the track rails, the equipment being arranged so that the transformer secondary windings alternately supply impulses of energy to the track rails, one of said secondary windings having a substantially larger number of turns than the other of said secondary windings, whereby the energy supplied from one of these windings is of substantially higher value than that supplied from the other of said windings so that the energy supplied to the track rails is predominantly of one relative polarity and is effective to operate said track relay.

6. In a railway signaling system, in combination, a section of railway track, a direct current track relay having a winding connected across the rails of said section, said relay being of a type which is responsive to energy of one polarity only, a track transformer for said section, and means including a unidirectional impedance element for supplying from said transformer to the rails of said section alternating current in which impulses of energy of both polarities are present in substantial magnitude and in which the potential of the impulses of energy of said one relative polarity is substantially higher than that of the impulses of energy of the other relative polarity.

7. In a coded railway signaling system, in combination, a section of railway track, a direct current code following track relay having a winding connected across the rails of said section, said relay being of a type which is responsive to energy of one polarity only, a track transformer for said section, means including a unidirectional impedance element for supplying from said transformer to the rails of said section alternating current in which impulses of energy of both polarities are present in substantial magnitude and in which the potential of the impulses of energy of said one relative polarity is substantially higher than that of the impulses of energy of the other relative polarity, and a coding device having a contact controlling a circuit for supplying energy from a source of alternating current to the primary winding of said track transformer.

8. In a coded railway signaling system for use in track stretches over which are operated vehicles carrying signaling apparatus responsive to the flow of coded alternating current in the track rails, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a forward and a rearward section, each section having a direct current code following.

track relay having a Winding connected across the rails of the associated section adjacent the entrance end thereof, said track relays each being I of a type which is responsive to energy of one polarity only, the track relay for the forward section being responsive to energy of normal polarity only and the track relay for the rearward section being responsive to energy of reverse polarity only, means for supplying to the rails of the forward section coded energy which is predominantly of normal polarity, a track transformer for said rearward section, means including a unidirectional impedance element for supplying from said transformer to the rails of said rearward section alternating current in which impulses of energy of both polarities are present in substantial magnitude and in which the potential of the impulses of energy of reverse polarity is substantially higher than that of the impulses of energy of normal polarity, whereby the energy supplied to the rails of said section is effective to operate vehicle carried signaling apparatus and is also effective to operate the track relay for said section, and a coding device having a contact controlling a circuit for supplying energy from a source of alternating current to the primary winding of said track transformer.

HOWARD A. THOMPSON. 

